hi all i have a n reg wagon turbo lately ive noticed a strange idling problem. when im driving and coming to a stop i put the clutch down and its idling at around 1200rpm put it in neutral and let clutch up and it drops to around 800rpm. its recently had a new oxygen sensor on as the emissions were miles out on its MOT, so was wondering could this be the MAF sensor playing up ?
thanks in advance for your replies

the car is prety much standard apart from a decat exhaust, a panel filter and a boost gauge.